Don't extend pistons until data is set. Fixes BUKKIT-2153

src/main/java/net/minecraft/server/BlockPiston.java

@@ -55,7 +55,7 @@ public class BlockPiston extends Block {
 
     public void onPlace(World world, int i, int j, int k) {
         if (!world.isStatic && world.getTileEntity(i, j, k) == null) {
-            // this.l(world, i, j, k); // CraftBukkit - don't extend arm of piston that doesn't exist
+            this.l(world, i, j, k);
         }
     }
 

src/main/java/net/minecraft/server/Chunk.java

@@ -417,7 +417,11 @@ public class Chunk {
 
                 if (l != 0) {
                     if (!this.world.isStatic) {
-                        Block.byId[l].onPlace(this.world, j2, j, k2);
+                        // CraftBukkit start - Don't extend piston until data is set
+                        if (!(Block.byId[l] instanceof BlockPiston) || i2 != 0) {
+                            Block.byId[l].onPlace(this.world, j2, j, k2);
+                        }
+                        // CraftBukkit end
                     }
 
                     if (Block.byId[l] instanceof BlockContainer) {